Wednesday, January 22, 2014

Hominin Evolution

While nature writers, including myself, have long used the term hominid to refer to humans and our post-ape ancestors, the more proper term is now hominin; the term hominid now encompasses all primates from ancestral great apes to modern humans.

The human lineage split from gorillas about 9 million years ago (MYA) and from chimpanzees about 7 MYA. Though the fossils of a few transitional hominids have been discovered in Africa, dating from 5-7 MYA, the first hominins are, for now, officially accepted to be Ardipithecus (4.4 MYA, discovered in Ethiopia) and a diverse group of Australopithecines (4.5 to 2.5 MYA), found in eastern and southern Africa. Branching from the Australopithecines were the genus Paranthropus (2.7 to 2.0 MYA), known as the robust Australopithecus, and the genus Homo, 2.5 MYA (as Homo habilis) to the present. Homo erectus appeared about 2 MYA and was the first hominin to spread to Eurasia (by 1.8 MYA). Neanderthals and Denisovans arose in Africa about 350,000 years ago, migrating to Europe/western Asia and to eastern Asia, respectively.

Homo sapiens, modern humans, evolved by 130,000 years ago and began to migrate from Africa about 80,000 years ago. Our species reached Southeast Asia by 70,000 years ago, crossed to Australia 60,000 years ago and extirpated the Neanderthals and Denisovans from Eurasia, after interbreeding with them (see Human Hybridism), by 30,000 years ago. Humans crossed the Bering land bridge and perhaps the North Atlantic ice shelf to reach the Americas by 20,000 years ago. Whether we are the last hominin or will evolve into other species will be determined by future anthropologists.